A combustion staging system is provided for fuel injectors of a multi-stage combustor of a gas turbine engine. The system has a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows to perform pilot-only and pilot-and-mains staging control of the combustor. The system further has pilot and mains fuel manifolds which respectively receive the pilot and mains fuel flows. The system further has a plurality of mains flow scheduling valves which distribute the mains fuel flow from the mains fuel manifold to mains discharge orifices of respective injectors of the combustor. The system further has servo line which extends to the mains flow scheduling valves, the servo line being controllably fillable with pressurised fuel to change the pressure in the servo line relative to the pressure in the mains fuel manifold. Each mains flow scheduling valve has a chamber containing a movable piston, the chamber to a mains side of the piston being fed by the mains fuel manifold, and the chamber to a servo side of the piston being fed by the servo line. The piston has an open pilot-and-mains position which allows flow out of the mains side of the chamber to the mains discharge orifice of the respective injector. The piston is biased towards a closed pilot-only position which prevents flow out of the mains side of the chamber to the mains discharge orifice of the respective injector. The piston is movable to the closed position under an increase in pressure in the servo line relative to the mains fuel manifold.

A combustion staging system has: a splitter; pilot and mains fuel manifolds; mains flow control valves; and fuel servo line. Each mains flow control valve has a chamber containing a piston, the chamber to a piston mains side fed by the mains fuel manifold, and the chamber to a piston servo side fed by the servo line. The piston has an open pilot-and-mains position allowing flow from the chamber mains side to the respective injector mains discharge orifice. The piston prevents flow from the chamber mains side. The piston is movable under a pressure change in the servo line relative to the mains fuel manifold. The system has a servo pump and a hydraulic motor driving it. The servo pump changes fuel pressure. Motive power for the hydraulic motor is fuel diverted from a fuel pump high pressure output, the motor returning the diverted fuel to a low pressure input.

A combustion staging system has: a splitter; pilot and mains fuel manifolds; mains flow control valves; and fuel servo line. Each mains flow control valve has a chamber containing a piston, the chamber to a piston mains side fed by the mains fuel manifold, and the chamber to a piston servo side fed by the servo line. The piston has an open pilot-and-mains position allowing flow from the chamber mains side to the respective injector mains discharge orifice. The piston prevents flow from the chamber mains side. The piston is movable under a pressure change in the servo line relative to the mains fuel manifold. The system has a servo pump and a hydraulic motor driving it. The servo pump changes fuel pressure. Motive power for the hydraulic motor is fuel diverted from a fuel pump high pressure output, the motor returning the diverted fuel to a low pressure input.

A combustion staging system is provided for fuel injectors of a multi-stage combustor of a gas turbine engine. The system has a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows to perform pilot-only and pilot-and-mains staging control of the combustor. The system further has pilot and mains fuel manifolds which respectively receive the pilot and mains fuel flows, the mains fuel manifold being split into a primary line and a servo line such that each line receives a respective portion of the mains fuel flow. The system further has a plurality of mains flow control valves which distribute the mains fuel flow from the mains fuel manifold to mains discharge orifices of respective injectors of the combustor, both the primary line and the servo line extending to the mains flow control valves before reuniting. The system further has a servo pump operable to change the pressure in the servo line relative to the pressure in the primary line. Each mains flow control valve has a chamber containing a movable piston, the chamber to a primary side of the piston being fed by the primary line, and the chamber to a servo side of the piston being fed by the servo line. The piston is biased towards a closed pilot-only position which prevents flow out of the primary side of the chamber to the mains discharge orifice of the respective injector. The piston is movable under an increase in pressure in the servo line relative to the primary line to an open pilot-and-mains position which allows flow out of the primary side of the chamber to the mains discharge orifice of the respective injector.

A combustion staging system is provided for fuel injectors of a multi-stage combustor of a gas turbine engine. The system has a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows to perform pilot-only and pilot-and-mains staging control of the combustor. The system further has pilot and mains fuel manifolds which respectively receive the pilot and mains fuel flows, the mains fuel manifold being split into a primary line and a servo line such that each line receives a respective portion of the mains fuel flow. The system further has a plurality of mains flow control valves which distribute the mains fuel flow from the mains fuel manifold to mains discharge orifices of respective injectors of the combustor, both the primary line and the servo line extending to the mains flow control valves before reuniting. The system further has a servo pump operable to change the pressure in the servo line relative to the pressure in the primary line. Each mains flow control valve has a chamber containing a movable piston, the chamber to a primary side of the piston being fed by the primary line, and the chamber to a servo side of the piston being fed by the servo line. The piston is biased towards a closed pilot-only position which prevents flow out of the primary side of the chamber to the mains discharge orifice of the respective injector. The piston is movable under an increase in pressure in the servo line relative to the primary line to an open pilot-and-mains position which allows flow out of the primary side of the chamber to the mains discharge orifice of the respective injector.

A fuel supply manifold for a gas turbine engine includes a first manifold segment includes a first multiple of double-barrel fittings in communication with a primary fuel circuit and a secondary fuel circuit. A second manifold segment includes a second multiple of double-barrel fittings in communication with the primary fuel circuit and the secondary fuel circuit. The first manifold segment is connected to the second manifold segment.

A fuel supply manifold for a gas turbine engine includes a first manifold segment includes a first multiple of double-barrel fittings in communication with a primary fuel circuit and a secondary fuel circuit. A second manifold segment includes a second multiple of double-barrel fittings in communication with the primary fuel circuit and the secondary fuel circuit. The first manifold segment is connected to the second manifold segment.

A system of injecting fuel into the combustion chamber of an engine, including at least two fuel circuits, one permanent flow circuit and one intermittent flow circuit, fuel proportioning and distribution devices for proportioning fuel and distributing fuel between the two circuits and a controller. When an order to fill circuits with fuel after the circuit with intermittent flow has been drained is received, the controller is adapted to control the proportioning and distribution devices to obtain a predetermined fuel flow higher than the flow corresponding to the filling order and to supply the resulting surplus of fuel to the intermittent flow circuit for a predetermined duration.

A system of injecting fuel into the combustion chamber of an engine, including at least two fuel circuits, one permanent flow circuit and one intermittent flow circuit, fuel proportioning and distribution devices for proportioning fuel and distributing fuel between the two circuits and a controller. When an order to fill circuits with fuel after the circuit with intermittent flow has been drained is received, the controller is adapted to control the proportioning and distribution devices to obtain a predetermined fuel flow higher than the flow corresponding to the filling order and to supply the resulting surplus of fuel to the intermittent flow circuit for a predetermined duration.

A dual fuel heating system can be used in a gas appliance. A dual fuel heating system can have a fuel selector valve for selecting between a first fuel and a second fuel different from the first. The dual fuel heating system can include a regulator unit configured to regulate the pressure of the two different fuels. The selector valve determines which flow path for which fuel is open and which is closed.